Oftentimes structures with multiple wythes brick, stone, concrete block, or even timbers are separated partly due to wind loads. The wind loads can be applied in suction or compression. Finally, extra structure loading may be applied in the form of earthquakes, earth shifts, mud slides, and others.
Various techniques have been developed, primarily in the United Kingdom, for a method of inserting and chemically bonding stainless steel helical ties into wood and masonry to enable the repair stabilization of multiple wythe walls normally having cavities between the wythes. Cavities between the adjacent wythes can be very small. Sometimes even zero in a solid wall, which nonetheless requires reinforcing.
In a proper cavity wall, the cavity will usually be one inch or more. Sometimes in the United Kingdom such cavities will be as wide as five inches, but normally in the two to four inch range. In the United States the gap is commonly approximately one inch. One such technique is marketed under the trademark RetroTie. Normally the tie is inserted from the outside wall, and the tie is driven into the inner wall where the tie itself cuts a thread in the substrate due to its rotation while being hammered into the wall. With harder materials such as brick and concrete, a pilot hole is normally drilled from the outside prior to insertion. The drills used for the pilot holes are normally 4.5 mm diameter drills irrespective of whether the tie is 6 or 8 mm in diameter. With certain softer materials such as soft wood, lightweight concrete, and such more unusual materials such as clay, no pilot hole is needed for that thickness.
The tie may be loaded into the insertion tool and a certain length left projecting for concluding the insertion. This length is determined by the needs of the job. Generally softer material requires deeper penetration. When the tie is inserted the amount of tie protruding is driven fully into the inner wythe, that is, the end of the support tool touches the inner wythe. After driving the tie to the required depth in the inner wythe, the outer end is lying in a clearance hole, which is ten millimeter for a six millimeter tie, or twelve millimeter for an eight millimeter tie. A plastic sleeve is pushed over the tie and positioned adjacent to the cavity and thereafter bonding takes place by inserting in the outer wythe a bonding agent such as a polyester or epoxy resin. Exemplary of the foregoing are European Patents 0150906 and 0171250BT.
An alternative for this technique employs reinforcement bars or threaded bars which are chemically bonded into both the inner and the outer wythes. Also, ties are inserted which may use expansion anchoring techniques or anchoring techniques to fix both ends or with expansion at one end and a chemical at the other. Either one or both wythes have the chemical bonding applied.
The anchoring system as described is comparatively expensive, oftentimes too stiff to permit differential movement between the wythes which occurs during the natural expansion of inner and outer wythe due to temperature and moisture variations. On the other hand, ties sold pursuant to the trademark Helifix described hereinafter have both axial load carrying characteristics and offer lateral flexibility. Moreover, they have a built-in ability to shed water that might attempt to migrate from the outer wythe to the inner wythe.